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02-13-2012 | 05:28 PM

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rctech2k7

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RE: Adding caps to esc???

Quote:

ORIGINAL: Von Ohain

I think this thread needs some clarification, so here comes my opinion, as a Bc. S. on electrical engineering.

1. The sole purpose of the capacitor is to protect the FETs from induced voltage spikes from motor and wiring harness.
The energy storage effect is neglible in this situation, because each capacitor stores so little energy, and the motor consumes heaps of it.
The capacitors has no practical effect whatsoever on the boat getting up on a plane, when you slam open your throttle.
The huge power surge will drain the capacitors nearly instantly and the voltage drop will happen anyway with no practical effect whatsoever from capacitor choice.
The capacitors task is to work as a 1st order filter together with the resistance of the wiring harness.
http://en.wikipedia.org/wiki/Low-pass_filter

2. The inductance on the wiring harness is NOT dependent on wire length. You do not have to use more capacitors if you use longer wires.
Inductance is determined by the closed loop area of the wiring harness, and if you use long wires, all you have to do is to strap the wires close together to keep the closed loop area small, and hence keeping inductance unchanged.
http://en.wikipedia.org/wiki/Inductance

Strapping the wires together also has the effect of creating greater capacitance in between the wires, further eliminating the need for any extra capacitor.
http://en.wikipedia.org/wiki/Capacitance

3. Do not ever buy a capacitor from Castle, or Etti, or anything like that. All they have done is soldered down some very generic electrolytic capacitors to a PCB board, stuck a badge to it, and charging you 50 times the price of what the chinese OEM does. There does not exist any ''hobby grade'' or ''hobby brand'' capacitors, so don't throw any money in that direction.

4. there is a very significant difference between brushed and brushelss here aswell.
A brushed motor will produce much higher voltage spikes than a brushless because of the way that an ESCs FET will allow internal closed loop bleeding of the voltage spikes, which the mechanical commutator of a brushed motor does not.
CC, which of course is very keen to sell their capacitors, fail to mention this.
CC also fail to mention that the inductance of extended motor wires is very easily kept down by simply strapping the wires together, keeping the closed loop area down.

Well said my fellow BSEEng'r. I know it's not that easy to deal with a lot complex analysis and calculation from this degree. How was laplace transformation?

Capacitor has lot of function from small micro electronics including RF ckt, RLC, etc. up to industrial application. It is one of the most common devices used in electric circuit analysis. Widely used in electrical engineering application such as power factor correction, transmission line improvement, etc...

Capacitor simply charges when current pass thru it. Using DC supply, initial current is extremely high (based on supply voltage, initial capacitor voltage and their resistance) then drops to zero, time is based on the time constant from product of resistance and capacitance. When used in AC ckt because of its characteristic it produces reactance based on supply frequency. The higher the frequency the lower the impedance is. The current of the capacitor ckt leads the voltage phase by quarter of a cycle or 90 deg. Most industrial system produce lagging power factor. It caused by the total inductive load mostly like motors. This makes the circuit inductive in nature, the total KVA consumed is a higher but by using capacitor it minimize reactive power and only left is true power which we are using. The total current power consumption is lesser therefore lesser amps, system is more efficient and can handle more loads.

In the case of our ESC with long distribution line from the battery it function as a filter and also as improving voltage regulation. Longer line produce higher resistance, the line itself has very small inductive reactance produce by high frequency noise from its load by using capacitor as I mentioned at high frequency it becomes low impedance therefore eliminating this electrical noise. As the nature of the line as inductive it produce high impedance at high frequency including changes in line current. By using capacitor it store the energy drops on the line during that changes, stabilizing and improving voltage regulation even at high rate of current change.

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